Manual range gate for stroboscopic indicators



Dec. 9, 1947. A. M. SKELLETT MANUAL RANGE GATE FOR STROBOSCOPICINDICATORS Original Filed Oct. 9. 1943 2 Sheets-Sheet l Dec. 9, 1947. A.M. sKELLl-:TT

MANUAL-RNGE GATE FOR STROBOSCOPIC INDICATORS 2 Sheets-Sheet 2 OriginalFiled Oct. v9. 194:25

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Patented Dec. 9, 1947` IVIANUALv RANGE GATEVFQR S'IRQBO-V SCOPIC.INDICATORS.

Albert M. Skellett, Madison,` Ni JL, assigner to Bell r[TelephoneLaboratories, Incorporated, New York, N; Y., a` corporation of'New YorkOriginal application October 9,1943, Serial` No,

;o5,s73. Divided-1 ana thisl applieanonpoyemser s, w45, serialV No.627,493

apiiieation is ad'lvisioh of my appending application Serial. No.`505,673, filed october 9, 1943, assigned to the same assignee as thepresent application. lihe invention claimed herein re'- late's to amanuali ran-ge gate an illustrative embodiment of which is describedherein in connection. with a stroboscopio indicator such as is disclosedthe. said application Serial No...

505,673.. The present application also discloses a scale changing systemwhich is claimed in my copending application Serial No. 627,491, led'November 8f, 1945,. and assigned to the same assignee as the presentapplication'.

The stroboscopic type of indicator is designed 'to replace thecathode-fray type of indicator common-1y used in radar systems. Thestroboscopic indicator is based on the stroboscopic` illumination .ofmoving or rotating scales and dials, the ashes of lightA being set onby' the received reflections. The range, azimuth, and elevation readingsmay appear in numerical form in Windows as if the scales on which thenumbers are laid out were stationary at the correct values for thereflecting object in question. Two-di mension'al eld images such asmap-likev representations in polar coordinates may also be provided likethose produced in cathode-ray tubes but of greater brilliance and size.VThese may or may not employ screens in which the glow persistsmomentarily after illumination. Automatic switching may be provided sothat the apparatus assigns reflections received froxna plurality ofobjects to diierent windows which give simul tankeous readings.V

The invention has among its advantages simplicity, increased ruggedness,W voltage operation, increased accuracy.

A further advantage is the low speed of the rotating parts, which neednot exceed 1800 revo-- lutions per minute;

An object ofthe invention is to reduce personal error in reading therange, azimuth or elevation of the reecting object, particularly in thecase of an unskilled observer.

As used in radar indicators the cathode-ray tube operates by moving apencil of electrons over a stationary scale, the electron beam beingmodulated Vat each sweep to give an indication at the same xed positionon the scale. Thus an apparently stationary -mark is observed. The

stroboscopic type of indicator operates on a re- The scale moves atYhigh speed past a iixed index and the illumination ofthe scale ismodulated s o as to give a ash .of light Whenever the correct Dart of,thejsiale is opposite 2V the index. The effect upon the observer is thesame in either case, namely, the appearance of a stationary mark on astationary scale.

In measuring rangeby reflected pulses it has been found practical tousea scale rotating in synchronism With the outgoing pulses and making onerevolution per pulse. The reasons for this are, first, that the speedrequired o f the rotating scaleis too high, and second, that it is notpossibleto. synchronize a rotating scale with the outgoing pulses insome radar systemsbecause the pulses are not emitted at a uniform timerate'.

In accordance with the invention, lovi speed scales may be used and aconsiderable amount of jitter or irregular spacing of the outgoing`pulses maybe tolerated.

For the azimuth or elevation scales it is en tirely practical tosynchronize the scales with the motion of' the antenna. At therelatively slow speeds of the azimuth and elevation scales the flickerof the flashes may be observable in some cases but this Will present noserious d iiculty since the overall effect is that of a stationary dialor scale illuminated with intermittent rather than steady light.l

In the drawings, Fig. 1 is an elevational View of the indicator panel ina one-dimensional indicating system embodying the invention; and

Figs. 2 and 3 constitute a schematic diagram of the electrical andmechanical apparatus associated with the panel of Fig. 1, when thesegures are arranged as in Fig. 4.

One embodiment illustrative of the invention is shown in Figs. 1 to 4,inclusive. This embodiment is restricted to measurement of a singledimension, namely, the range. In a class A representation, horizontalexten-sions indicate range or ydistance and a vertical line or markindicates the location of an object at a distance Vshown by thehorizontal position of the line or mark. Provision is made to display aclass A representation of the ranges of several distant objectssimultaneously against a calibrated scale from which the approximaterange of each object may be read directly, for example in yards. Thereis also provided a single range dial from which Vmay be obtained a moreaccurate reading of the range of any desired one of the distant objects.A manual range gate is provided and associated with a movable marker inthe class A indicator so that a particular object, the range of which itis des sired to register on the ran-ge dial, maybe readily selected. Theobject selected may be changed for another whenever desired by repeatedmais provided whereby the precision of the range measurement indicatedby the range dial may be increased by a predetermined factor whendesired, a factor of ten being preferred. The range dial and the class Arange indicator comprise rotating elements each of which isstroboscopically illuminated only at those instants when it pre sents acorrect range reading.

Fig. 1 shows the external appearance of the device as it may be arrangedfor the convenience of an operator. A portion of the indicator panel isshown at and is provided with windows |0| and |02 which may havesuitable frames or bezels. Behind the window |0| is mounted a range dialcomprising a drum |03, preferably translucent, upon which are placeindications such as a numerical scale of ranges. Provision is made forrotating the dial |03 and illuminating it stroboscopically when acorrect range indication appears within the window |0| at a stationaryindex |04 that may be placed before the dial |03 to fix the exact pointof reading. Behind the window |02 is provided a rotating drum |05 with ahelical mark which is made to appear, when stroboscopically illuminated,as a vertical or nearly vertical line segment showing through thewindow. A stationary scale |05 is provided for reading the position ofthe line segment when illuminated. The drum |05 may be illuminated anumber of times during each revolution to produce a plurality of linessuch as are shown at |01, |08 and |09 to indicate the ranges of objectsat different distances. An arbitrarily movable line H0, which may bedistinguished from the lines |01 to |09, inclusive, in any suitable wayas for example by a differentY color of illumination, may be providedunder manual control of a knob to aid in selecting one of the distantobjects the range of which is to be indicated more precisely by thereading of the dial |00. Another knob l I2 may be provided to control anexpanded scale and the associated indication of a separate dial H3mounted next to the dial |03 and appearing within the window |0|. Thedial ||3 is stationary except when rotated manually by means of the knob||2 and is illuminated together with the dial |03 by the stroboscopiclight source. The mechanism associated with the panel |00 will bedescribed hereinafter with reference to Figs. 2, 3 and 4.

The manner in which the system is manipulated by the operator may bedescribed with reference to Fig. 1, it being assumed that the internalmechanism is operating and has been properly adjusted. First, it will beappreciated that the external appearance of any strobe-scopicallyilluminated device will generally differ from the external appearance ofthe same device when viewed in ordinary illumination. For convenience inexplaining the operation of the system and at the same time to make theview in Fig. l consistent with the other figures, it has been chosen tomake Fig. 1 a composite View. The window |02 is assumed to be viewedwith the drum |05 revolving and stroboscopically illuminated. Theoperator sees in the window |02 the marks or lines |01 to H0, inclusive,as shown in Fig. 1. The dial |03 is shown as if stationary and understeady illumination. As this dial actually is revolving along with thedrum |05 at a rapid rate it would appear blurred and unreadable unlessthe movable range mark ||0Ywere placed in,coincidence with one of thelines |01 to |09, inclusive and the knob H2 were properly set as exlnipulation of the range gate. An expanded scale plained hereinafter. Inusing the system, the operator, observing the lines |01 to |09,inclusive, decides which one of the objects represented by these linesis of special interest and he turns the knob to move the mark ||0 tocoincide with the desired line and adjusts the knob I2 properly asexplained hereinafter. The dials |03 and ||3 are then stroboscopicallyilluminated to show the range of the selected object legbly andapparently stationary opposite the index |00. Another object may bethereafter selected by turning the knob to bring the mark H0 incoincidence with the second selected line and by readjusting the knob l2if need be, when the stroboscopic illuminatio-n of the dials |03 and 3will change to display the range of the second object. Within the window|0 an illustrative range reading is shown on the expanded scale,indicating an object at a range of 83,500 yards. This reading could beobserved by bringing the mark ||0 to coincide with the line |09. Todispense with the expanded scale and use what is commonly called themain scale, the knob ||2 may be turned until a numeral 0 appears on thedial ||3 and a step further to operate a switching mechanism which maybe mechanically coupled to the knob ||2 to switch over the electriccircuit from a condition termed. the expanded scale condition to onetermed the main scale condition as hereinafter described.

Figs. 2 and 3 show the mechanism and circuits behind and associated withthe panel |00 of the device shown in Fig. 1.

In Fig. 2 a pulsing circuit 200 is shown connected both to an oscillator20|, preferably of ultra-high frequency, and a square Wave generatortube 202, which with connected elements will be referred to as thestart-stop circuit. The oscillator 20| is connected to a suitableradiating system such as a dipole antenna 203 mounted at the focus of aparaboloidal projector 200. The output of the start-stop circuit isconnected to the grid circuit of a vacuum tube 205 in the anode circuitof which is connected a timing resistor 203 and condenser 201. Thecondenser 207 is also connected in the input circuit of a square wavegenerator tube 208, which serves as a narrow automatic range gate. Forthe reception of electromagnetie waves there may be provided adirectionally selective receiving system comprising a dipole antenna 200mounted at the focus of a paraboloidal reflector 2|0. The antenna 209 isconnected to the input of a radio receiver 2| the output of which iscombined with the output of the tube 208 in the input circuit ofamplifying tube 2| 2 In Fig. 3 suitable power terminals 300 are shownconnected to a motor 30| to the shaft of which are keyed the dial |03,the drum |05 and a pair of rotary switches or commutators 302 and 303.The commutator 302 is connected with a source 304 of direct current'anda timing resistor 305 and either one of two condensers 306 and 301. Thedial |03 may be translucent and may have mounted within it a flash lamp308l which may be a neon lamp. The drum |05 may be opaque except for ahelical slot 303 which either may be open or may have a filling of atranslucent material. Within the drum |05 may be mounted flash lamps 3|0 and 3| preferably giving different colors of illumination such as aneon lamp 3|!) and an argon lamp 3| The broad principle of operation andthe salient features of the structure of Figs. 1 t0 3, inclusive, willrst be briefly given before presenting a more detailedi descr-'intiemThe;Y powersupp1iedftof-the terminals 30'0 may be--eo'nvenientlyi'ntheformf of G01cycle alternating current l toi drive acommon type ofi motorata speed-ofA approxi'matelyy 1800l revolutionswper minute, that isabout thirtyrevolutions per second.-

particular speedais'not' essential'butf-'hasl beenfoundboth suitable andconvenient-.k Themotor- 30|# drives the dial |03, theA drumI'GSand'the"commutatore 302 and 303 directly at'this speed. At apreferably more rapid rate", say 2001 to-1,000 or` more` time'sper'second,

the pulsingA circuit' 200 briefly energizes the radioVv transmitterv |1to deliver a short trainL of waves to'fthey antenna 203i' whichtrainis-proiectedv asa pul'se of! electromagnetic waves fromthe`projector 2042.h Simultaneously with the energizationofthe radio--transmitter; the pulsingt circuit energizes thet tubel 202i' togeneratea square-topped'pulse usedv to blockf'the tube 205 andfstart a'-charging current in the: resistor" 25053 andl condenser 20T. The] tube205i and;| associated timing elements will bel-hereinafter' referred'to-as' the fast timing cir,-A cuit.;V The timeconstant of; thel circuitis preferably so pnredesi-gned'thatV the potential ofthe condenser T`will'pass through a suitable range of values at? a' substantiallylinearY timerate during the' brief time requiredV for an electromagneticpulseftotravel from'tli'eAprc-j'ector 201Mothe most distant-object'tlierange ofiwhiclr'l` is to be measuredandtoreturn tothe-reflector 2| il:Thecornut'ato'r 3 02`is arrangedtoiconnectthe'battery 361%4 to'the othertiming circuitf comprisingthe resistor 305 and the' condenser 306 tocharge the condenserseat a: rate relatively 4slow compared with the"condenser 2 0 to cover alsiinilar suitable range ofipotentials!onthecondenser 305 during a single revolution of the commutator: This lattertimingi circuit" will hereinafter :be referred to' as the slovftimingcircuit; Due to the relatively slow rate of revolution ofthemechanicalfsystem; it is permissible to facilitate-the description byassuming for the time being that the dial |03 and drum |95 remainstationary' during the time between two pulses ofthe pulsing circuit200. It is also permissible at tl'lispoint in'the description to assumethat the potential ofthe condenser 305 remains constant during' theinterval between two pulses: Provision is` madeto" compare thepotentialof the condenser3'05 andthe potential ofthe condenser 20T in thegrid-cathode circuit of the tube-2082 At some instant duringthe periodbe tween successive pulses tliepotentials of the condensers- 305" andY20Twi1l be of the proper rela;-

tion' to each other tounblock the tube 208 and thereby initiate' asquareetoppe'd pulse therein. The circuit ofY the tube 200 is preferablyso designed that the square-topped pulse produced is one' of relativelyshort duration. The tube 208,

however; does not directlycnnect' with the flash. l'an'lpsibutmerely'energizesor sensitizes the input circuiti 0f theanlplifylhg:tubel2`lr2.` The tube 2|2 will operate to ilash thelamps3|l8v and?, l0 only if a" refiectedpulsefis' received by the" radioreceiver opposite? the sam'etrange: reading? on'th'e: scale I 03assis.simultaneouslyappearingonzthe dial?A |03=l and tl'iersetting oflthe manual rangegateagreeg.

'llh'e'l'amp Silllon' the other'hand is preferablyfnot; under`the-control ofthe 4range gate?so'.tha'titm'ayfl ashv wheneverA the:range of` a: distanti objects agrees with the* position or the slot`309IWith4 re-Y erablyentirelyl independent-ofthe reflectedpuls'es andiof' the' action offthe'ftubef 25|:Z4and may be con;` trolledl solelyby-'the setting of the range" gatet flashv once per revolution of thedrum |055 themechanic'al' systems, the shaft and:attach;K ments will.no'f longer be consider'edl asfstanding* stilla DuringV eachl intervalfbetween pulses the? diallme; drum: le5.;anditnefcornnutators 302 andY303 will have moved a srnallifra'cti'onlof a revolu-V tion and thepotential of" theL condenser 3051i will liaveiiricreased'iaccordinglytThe dial lliandthe' drunlE ||l5f have advanced tot slightly higlfl'erlIrangeireadingl Thecrit'ical relation ofpote'ntialsr ofV the"condensersl20l' and 306 now!occursatia` slightly later epoch withrespecttolthe star-t of the outgoing pulse' from' the projectori 202i? Asia"result-the' tube Zil'iwillenergize the tube 2T|2 atal correspondinglyVlater epoch andthe-- lampa-308 and 310 Will'l'ash onl'yfin-responsetolaniincoming reflected pulse froma somewhat'more'distant-ob# ject, therange of. which corresponds to the new reading of the diallll3`anddrurn|05. Accordnglyn eachsucceedingcycle of thepulsingfcirs cuit 200S'thelamp; control circuits.will'be'energizedi at the particular epoch whichcorrespon'dsi to; the:r range reading simultaneously presented' atithe:Windows bythe dial |03=and=t=hedrum |05. During, each revolutionof themechanical-system the .lamprcontrolcircuits will have been briefly energize'd successively at a succession ofrang'e read^-v ings distributedoverf the total range of' the' apparatus; When) the range readingcorresponds' to? therang'e" ofan object the reflected pulses from thatTobject Will:- be" enabled toffla'sh theV lamps at` leastionce during therevolution; As lthe'spee'd ofY rotation issuflicient'to'providetSO iflashes persec-v ond a1substantially flickerlessfscalereading is obftained.`

In` order that no pulsesb'e lo-st due to` being returned from'l objectshav-ing ranges that-lie be tween the successiverange readings for whichthe'` lamp. control circuits are energized, theaut'omatic vrange gateshould be open each time fora sum'- cient interval to admit allreturning pulses fromv objectsin a Zone of a certain width. The ratioof" the frequencies of the fast and slow timing cir. `cuits' determinesthe width of the Zone' to loe-in'- cluded by the range gate, or, as itmay be more briefly' termed, the width of the range gate. Thisshouldbeas wide as the difference in' the successive range readings for whichthecircuit's are energize'dto insure that allY reflected pulses willoperate the ash lamp. For example, with a motor' speed of 30 revolutionsper second anda pulsing. rate'of 2000 pulses per second, the rangeVgateshould have a width of about 11/2 per cent of the maximum range, or1500 yards in 100,000` yards. For an expanded scale of "ten times thesensitivity of the main scale, the range gate width in this example maybe reduced to one-tenth or yards. The actual readings may bemoreaccurate than the frequency: ratio indicates, due to the fact thatunless the frequencies are jexactly commensurate succeeding readings onthe same the# lampen 8v isipreferablyf" range will vary slightly and theeye will naturally read the average of the values presented by thescale.

The lamp 3I0 will flash once per revolution for each received pulse andwhen several pulses are received from objects at different ranges thelamp 3|0 will flash when the slot 309 is opposite each of a number ofdierent readings on the scale |06 producing a plurality of lines such as|01 to |09, inclusive. The commutator 303 will ash the argon lamp 3I|once for every revolution of the drum |05 at a particular angularposition which may be controlled by means of the knob III to produce anarbitrarily movable mark I I of a different color from the lines |01 to|09, inclusive. By moving the mark IIO to coincide with one of the linessuch as |01 to |09, inclusive, the lamp 308 will be made to ash to showa precise reading of the range corresponding to the particular lineselected by the operator.

The purpose of the expanded -scale is to cover a restricted group ofranges With a more precise balance of voltages in the input of the tube208 as well as with a narrower range gate. The particular portion of thescale to be covered by the expanded scale is indicated by the dial |I3which places an additional digit in front of the reading of the scale|03 by means of a mechanism which Will be more fully describedhereinafter.

The circuits shown in Fig. 2 will now be described in somewhat greaterdetail,

Start-stop circuit The start-stop tube 202 may contain, in a singleenvelope, if desired, two triodes 2I3 and 2|4, the triode 2 I3 includinga cathode 2 I 5, a grid 2 I 6, and an anode 2I1 and the triode 2 I4including a cathode 2|3, a grid 2|9 and an anode 220. A supply source 22I, such as a battery, may have its negative terminal grounded as at 222.The positive terminal of the source 22| may be connected to the anode 21 through an anode load resistor 223 as well as directly to the anode220 and through a grid load resistor 224 to the grid 2 I 9. The cathodes2I5 and 2I8 may be connected to ground through cathode resistors 225 and226. The pulsing circuit 200 may be connected to the grid 2|6 by ablocking condenser 221. A grid resistor 228 is preferably connectedbetween the grid 2I6 and the common terminal of the cathode resistors225 and 22B. A coupling condenser 229 is provided between the anode 2|1and the grid 2I9.

In the operation of the start-stop circuit, the triode 2| 4 is normallyconducting because of the connection of the grid 2I9 with the positiveterminal of the supply source 22| through the resistor 224. Theanode-cathode current of the triode 2 I4 flowing through the properlyproportioned resistor 225 provides a blocking potential upon the grid2I5 which renders the triode 2|?, normally non-conducting. Theconnection of the grid 2|9 to the positive terminal of the source 22|through the resistor 224 renders the grid potential positive with theresult that grid current flows through the triode 2I4 and adds to thebiasing current in the resistor 225. The triode 233 has substan tiallythe full supply voltage impressed across between its anode and cathodealthough, as aforementioned, anode current is blocked by the negaM- tivepotential impressed upon the grid 2|5 by the current flowing in theresistor 22 5. This condition of the start-stop circuit is a stable onebut it may be disturbed by the receipt of a pulse from the circuit 200.

The pulsing circuit 200 is preferably arranged to impress a pulse uponthe grid resistor 228 through the blocking condenser 221, the pulsebeing of such polarity as to render the grid 2 6 more positive withrespect to the cathode 2|5. The pulse is preferably of sufficientstrength to overcome the negative bias impressed upon the grid 2| 6 bythe resistor 225, thereby rendering the triode 2|3 conductive. The flowof current from the source 22| through the resistor 223 and theanode-cathode circuit of the triode 2|3 produces a drop in the potentialof the anode 2I1. As a result, the charged condenser 229 begins todischarge through the resistor 224 and at the same time the condenser229 effectively places a negative bias upon the grid 2I9, therebycausing the triode 2M to cut olf its own anode-cathode current. Thecessation of the current in the triode 2M removes some of the negativebias from the grid 2|6 and enables the supply source 22| to maintain theanode-cathode current in the triode 2|3 even though meanwhile theactivating pulse from the circuit 200 may have ceased. The condenser 229continues to discharge through the resistor 224 and when suiicientlydischarged, the triode 2M again becomes conductive and its anode-cathodecurrent restores the negative bias in the resistor 225 to cut off theanode-cathode current in the triode 2|3, thereby returning thestart-stop circuit to the original stable condition. The time requiredfor the cycle of operations in the start-stop circuit is determinedmainly by the capacitance of the condenser 229 and the resistance of theresistor 221|. The cycle may be repeated by supplying successive pulsesto the grid 2|5 from the pulsing circuit 200. The start-stop circuitdevelops a good square-topped wave between the cathodes 2|5 and 2|8 andthe ground 222 which Wave may be impressed upon the grid of the triggertube 205 by means of a blocking condenser 230 and a grid resistor 280.

Fast timing circuit The fast timing circuit comprises the vacuum tube205, the resistor 206 and the condenser 201. The tube may be a pentodehaving a cathode 23 I, a control grid 232, a screen grid 233, asuppressor grid 232 connected to the cathode, and an anode 235. Thecathode 23| may be grounded and the anode 235 may be connected to thepositive terminal of the source 22| through the resistor 206.

In the operation of the fast timing circuit, the grid 232 normallymaintains the tube 205 in a conducting condition due to the potentialdrop across the resistors 225 and 22B being balanced with respect to thegrid 232 by a charge on the condenser 230. When the potential across theresistors 225 and 226 falls during the operation of the start-stopcircuit, this drop in potential transmitted through the condenser 230impresses a negative potential upon the grid 232, thereby blocking thetube 205 and permitting charging current to ow to the condenser 201through the resistor 206. At the end of the square-topped pulse when thepotential difference across the resistors 225 and 225 is restored, thegrid 232 returns to substantially ground potential, rendering the tube295 conducting and permitting rapid discharge of the condenser 201through the tube 205.

Automatic range gate The automatic range gate comprises the square wavegenerator 208 and associated circuits. The tube 208 may contain, in asingle envelope, if desired, two triodes 235` and 231, the triode 236includingY a cathode 238, a control grid 239 and @resetear eaneanodei12-4.0 and :fthe :triode 231 @including .a nathoded-e!a:.contrQ11gridi-2 2.2 and anzvanode 2123. zlhecathode :g2 fil ,-may be.directly v.grounded Vand jtheicathode `23,8 :may :be connected toground gthroug'he coupling zcOndenser 245. The Aanodes .241and52i3-maybeconnectedto the positive terfminal :of r`the source :221 "through,anode circuit :resistors .'2jl5-and v225, respectively. The anodes ",245-and 213;3 may be cross-connected to the vgrids e242 .and 239,`respectively by coupling condensers .2,41fandc2i3. Thev grid 239 Ymaybe :connected to the positive terminal ofthe condenser-1:2 E31 through.alcoupling resistor e249. The grid 2132 may :be fconnectedto groundthrougheitherzone of-tWo resistors 250 and 25l under the-control vof a:switch-252.

lnthe operation Vof the automatic .rangesgate .'thepotential ofthegcondenser 2017is continuously .fcomparedwith the potential of-aselectedone fof Vthe condensers v30,5 Aand 301 in the grid-cathode .tu;circuit:of the tricde 1.236. The rpotential of ithercondenserZl'i'l'actsby virtue of direct connection in :the`.grid-cathode circuit, while the potential of condenser 305 or 301 isimpressed upon the cathode 238. The Ipotentialof the cathode 238 gisthus changing ata slow rate and the potenitial of the. grid 239 ischanging at the'fast rate. .'At the start of -each rfast cycle the-grid`potential @,isrfmore -negativewith respect to that of zthe cathode 238thanfthe cut-off voltageof vthe triode .and as it rises .this cut-offpotential is reached fandtthe-triode236 startsto conduct. Before thislcriticalpotential relation is "reached the triode 23.1lisfconductingdue tothe grid 242 4being connected tothe cathode 24| through one offth:resistors 25E] and 25l, and the'coupling condenser '.2151 `containsacharge :of substantially fthe full voltage of the source `221. 'Whenthe triode. 235 `becomes conductingyitsanode potential falls Vduetofathe flow of current'in the "resistor `255, and this fpotential dropis `impressed `on vgrid '242 lthrough condenser 221, thereby immediatelyblocking the triode 231. The condenser'ZG-lrapidly dschargesthroughthe-resistor 25B or 25| 'removing 'after :a denite interval the blocking'potential from the grid242 and permitting cur- Jrentito flow again. Itwill be noted thatwhile i the :triode :231 was blocked, `the couplingcon- :denser i243 vvasbeing Vcharged 'through the rersi'stors "243, 249`.andthe 'condenser 281. "'When -th'e 'triode 231 'has 'resumedconductivity, the charge `4on the condenser 248 is effectively thrown:across between the grid 1239 and the cathode 238 to form Valblockingpotential to aid in restoring the 1triode'236 to `the normal condition.The .generator 228 ythus produces a' square-topped pulse preferably ofbrie/f duration which is impressed upon the input circuit vof thehashing tube 212. "During the normal blocked condition :of fthe triode'236, the triode 231 isconductive -andhence the anode 253 may bearrangedto be :verylittle above the potential of the-cathode 2M.

"Duringthebrie'f period of blocking in the triode- .231,the anode223assumes substantially the full"v battery potential. anode 223 thusconstitutes a narrow squarelThepotential variation of the Jtopped Wave:of ipotential. `The duration yoi? the Flashing vcircuit The flashingcircuit comprises fthe tube 222 and associated ,elements. "IheAsquare-ttoppei control electrode 10 -v`vvave from the generator l208 isAimpressed upon :thefflashing-circuit through a-coupling` condensere253. The flashing tube -2l2 may contain, in a fsingleenvelope, ifdesired, two triodes 25d and 155, the triode.254 including a cathode256, a lgrid1-251eand .an anode 258 and the triode -255 including@Acathode y259, a grid 250 and an anode 251. The'ungrounded side of theradio Vreceiver A2li-.maybe connected tothe grid 251 through a couplingcondenser 4252-and the output of the automatic range gate may beconnected into the grid-cathode circuit of the triode 254 by means .ofthe Acouplingcondenser 253. The tube 2I2 .comprises tvvostagesr ofamplification. Normally fthe grid 251 is biased morenegative than-its[cut-.ofpotential so that echoes from'the'radio vreceiver `lcannot 'getthrough to operate the .flashing .lamps 358 and 3H). `When the `rangefgatefis impressed on this grid it brings its potentialto cut-off fandthe echoes, which are of pesitive potential canthenget through totriode255 .fvvheretheyare amplified fori-use in -triggeringoff.theeflashitubes 308 Vand 31B. Thusthetube=2l2 lis f operated -when :asignal `is received by the .radio--receiver2ll provided at'the sametime'lthe .triode 25.4 is unblocked by the-action of 'theitube '.268.

Flash lamps The flash lamps 308, 3l0 and 3| I are preferably .of .thethree-,electrode cold type. The tubes .358, 31.0 and 3H have anodes 3|2,VZilt and 3m, respectively, .all ,of which are-permanently con-'.nectedacross a .condenser 255 and va seriesind uctance 258 .through a.lead 315 and through .the .lead 3|.5 and -a -resistor 2.61 Ato ay.junction .point 254 in la potentiometer .across the source .2.2L Thetube .328 has a `pair .of .control .elec- .trodes `,316 .and-.31.1 andthe tubes 3l() Yand 3M have .corresponding .pairs of control .electrodes`{tl-B,3.l.i..and.32ll,.321l. Ground connection `is suplpliediover .alead .322 in a-.permanent connection tothe Ycontrol `electrode 31.8 .of`the tube 3H! .so .that .this tube Yvvill flash `Whenever -an exciting.potentialis impressed upon `its second control -electroderl Groundconnection issupplied to the controlelectrodes-SIB and 32B offthe tubes308 and 3l l, respectively, through a lead 323, a brush 324,rafconductive band "325 of the commutator `3113, -a v-brush `322 -toground at 321 only during the passage of the -b-rush A224 over vtheprojection 328 of Ythe lband V325. At allfother ltimes the brush 324connects the electrodes 3l5 and 322 through another brush 349 to adisablin'g ypositive potential such as is supplied by :a battery 350.The second control electrodes -2V! .and131f9-.of'the tubes 398 Vand 3H),respectively. .are --connected through a. lead 329 Vto a junction point265 in the output circuit of the flashing tube :212. These l:tubes v328and 312 receive over 'the `'lead 329 a dashing voltage upon receipt ofla reflected radio wave by the svstem at '.a time "when vthe Aautomaticrange gate is open. The control-electrode '32! ofthe tube 3H ispermanently connected tothe positive terminal of fa illustrated 'as -abattery. VThel battery i330 becomes eiective to-flash -the tube :311|whenever the ground eonnectionis appliedlto thevother 32!! by thecommutator 323.

lathe-operation of the tubes 322, 31E? and 3H it will kbeevident rcmftheforegoing description foftne connections that'the tubel l will beoperfated once duringeach Arevolution et the cornmutator when thebrush-322 crosses the project- J -ing=segnientif328- Thetubee?,willilash'provided a radio impulse is received while the automatic rangegate and the manual range gate are both set for substantially thecorrect range. The tube 3|0 will operate independently of the manualrange gate Whenever a radio impulse is received during the opencondition of the automatic range gate. Each flash of the lampsdischarges the condenser 266 which is then recharged at a denite ratethrough the resistor 261 and the inductor 268 in time for the nextflash.

Slow timing circuit The slow timing circuit comprises the source 300,the motor 30|, the commutator 302, the potential source 304, the timingresistor 305 and the timing condensers 306 and 301. The source 304 isconnected across a pair of serially connected potentiometers 33| and332. Assuming the potentiometers 332 and 33| to be set each on step 8 asillustrated, a circuit is formed through a ilexible lead 333 to theresistor 305, through a brush 334 on the commutator 302 to another brush335 and then through a lead 336, to one of the condensers 305 and 301and then through a lead 331 and a flexible lead 338` to step 8 of thepotentiometer 33| and thence to ground. The commutator 302 comprises twoconductive bands 339 and 340. The brush 334 runs continually on the band340 and a brush 34| on the band 339. The brush 335 runs upon the band340 except during a certain portion of each revolution when the brush335 rests upon a projection 342 which is an integral of the band 339.While the brush 335 rests upon the projection V342, the condenser 306 or301 is short-circuited. When, during the revolution of the commutator332, the projection 342 moves away from the brush 335, the condenser 306or 301 begins to charge through the resistor 305. The charging of thecondenser continues at a substantially uniform rate until the projection342 is again brought under the brush 335 when the condenser is quicklydischarged and made ready for a repetition of the charging cycle. Thepotentiometers 33| and 332 are preferably so arranged that the effectivecharging voltage is the same regardless of the steps occupied by thevariable contacts of the potentiometers.

Rotating mechanical system The commutators keyed to the shaft of themotor 30 The dial |03 and the drum are preferably xedly attached to theshaft by suitable V'means such as spider structures 342 and 343,respectively. The dial ||3 is preferably mounted freely on the shaft andmay be geared to the knob H2 in known manner as, for example, by meansof a suitable combination of racks and pinions. The brush 324 ispreferably mounted on a spider structure 344 which rides freely on theshaft and is geared to the knob through another suitable combination ofracks and pinions. The remaining brushes are stationary and may besupported in any suitable manner. The lamp 308 may be mounted inside thedial |03 and the lamps 350 and 3|| inside the drum |05. The necessaryleads to the lamps may be introduced through the space between the dial|03 and the drum |05.

Angular displacement of the rotating parts In setting the commutators302 and 303 and the dial |03 and drum 05 on the shaft, the followingconsiderations should be observed as to the relative angular positionsof these elements. The dial |03, in a system intended to measure 302 and303 are preferably showing at the window |0|.

ranges up to 100,000 yards will preferably have a scale reading from 0to 100,000 occupying a major portion of the periphery of the dial. Ablank segment, shown in Fig. 3 for clarity as one-sixth of the completecircle is reserved to cover the interval of time required for thedischarge of the slow timing circuit but this interval may be shortenedconsiderably in practice. The helical mark 300 occupies the sameproportional part of a complete circumference of the drum |05 as thenumerical scale occupies in the complete circumference of the dial |03.The dial |03 and drum |05 are to be set in such a relative angularposition that the reading of the dial |03 against the index |04 at thewindow |0| is identical with the reading of the mark 303 against thescale |06 at the window |02. The angular relation between the commutator302 and the brush 335, should then be such that when the trailing edgeof the segment 342 of the commutator leaves the brush 335, the dial |03registers Zero against the index |04. The angular position of thecommutator 303 on the shaft may be determined arbitrarily.

M ain scale When the expanded scale is not in use, the apparatus is saidto be operating on the main scale. The potentiometers 33| and 332 areeach provided with ten taps or positions, numbered from 0 to 9,inclusive, which are used with the xpanded scale. An additional positionM is provided adjacent to the zero position for use when operating withthe main scale and is directly connected electrically in thepotentiometer with the adjacent position 0. Potentiometer arms 345 and346 for the respective potentiometers 33| and 332 are provided and maybe insulatingly attached to a bar 341 in the rack and pinion systemoperated by the knob l |2. In using the main scale the knob l2 isrotated tobring the arms 345 and 340 on to the respective M positionso-f the potentiometers. This operation results in a rotation of the dial||3 through zero to one position beyond zero, at which position there isno number The switches 252 and a switch 348 controlling the selection ofthe condensers 306 and 301 are preferably mechanically coupled to one ofthe potentiometer arms 345 or 340 in such a manner that the switches 252and 348 are both operated Whenever the arm 345 passes from the zeroposition to the M position or vice versa. For the main scale, theswitches 252 and 348 are operated into the M position bringing theresistor 25| and condenser 301 into circuit for the main scale and theresistor 250 and condenser 306 for the expanded scale. In operation withthe main scale, one terminal of the condenser 301 is grounded so thatthe potential impressed upon the condenser 244 by the slow timingcircuit is simply the potential of the condenser 301. The resistor25|.is proportioned to give the desired width to the automatic rangegate. The reading in the window 0| is shown by the number appearing onthe dial |03.

Expanded scale In operation with the expanded scale, when one of themarks such as |01, |08 and |09 appearing at the window |02 has beenselected by the operator, the knob ||2 is turned to bring the rst digitof the range of the selected line into view in the Window |01. Forexample, if the line |03 is chosen (reading approximately 83,000 yardson the scale |03) the digit 8 is brought into view in the Window |0|, asshown in Fig. 1. This .opera- 13 l tion moves the potentiometer arms 345and 346 to the position 8 on the potentiometers 33| and 332, asillustrated in Fig. 3. It also operates the switches 252 and 348 to the9 position, bringing into circuit the resistor 250 and the condenser306. The condenser 306 is now in series with a potential providedbetween ground and position 8 of the potentiometer 33| and thispotential is added on to the potential of the condenser 306 in thecondenser 244 for comparison with the potential in the fast timingcircuit. The potential impressed upon the slow timing circuit is thesame regardless cf the position of the potentiometers, when, as ispreferable, the potential between each pair of'corresponding positionson the two potentiometers is the same. The resistor '250 is preferablydesigned to reduce the width of the automatic range gate to one-tenththe value used with the main scale. The condenser 306 is preferably madeten times the capacity of the condenser 301 so that during the period ofa single revolution the condenser 303 will acquire a potential onlyonetenth as great as that attained by the condenser 301 when using themain scale. The potential difference between two adjacent positions ofthe potentiometers is thus spread out by means ofthe condenser 306 tooccupy a complete cycle of the slow timing circuit. The reading in thewindow l0! is comprised by the reading of the dial H33 prefixed by thedigit exhibited by the dial Il'3.

In the system as illustrated, switching over to the expanded scaleexpands the range covered by the drum I and the images in the longwindow 102. The scale |03 will then represent hundreds of yards insteadof thousands as for the main scale and as the knob I l2 is turned theportion of the total range covered by the scale l 06 will be moved alongthe total range along with the indi-cation of the dial |I3.

What is claimed is:

1. A manual range gate comprising a rotatable commutator having a shortsegment and a long segment, a rotatable range scale, means to rotatesaid commutator and said range scale in synchronsm, two brushes makingcontact with said commutator, the rst of said brushes being stationaryand continuously in electrical contact with the short segment of thecommutator, and the second of said brushes being rotatably adjustablewith respect to the axis of said commutator and in electrical contactwith the short segment and the long segment alternately, means toilluminate said range scale, means connected to said commutator brushesto disable said range scale illuminating means while the said secondbrush is on the long segment and to sensitize said illuminating meanswhen said second brush is on the short segment, whereby the range valuefor which the range scale may be illuminated may be controlled byadjusting the angular position of said seccnd brush.

2. A manual range gate comprising a rotatable range scale, a fixed indextherefor, a rotatable commutator having a short segment and a longsegment, means to rotate said range scale and said commutator insynchronism with a predetermined constant angular relationship betweenthe said range scale and the short segment or" said commutator, twobrushes making contact with said commutator, the first of said brushesmaking uninterrupted electric contact with the said short segment, andthe second of said brushes making electric contact with the shortsegment and the long segment alternately, means to adjust the angularrelation between the said second brush and the said fixed index of therange scale during the rotation of said range scale and commutator,flashing means to illuminate said range scale and index, means connectedelectrically with said brushes to disable said nashing means wheneverthe said second brush is in contact with said long segment and tosensitize said flashing means whenever the `said second brush is incontact with the said short segment,

Vwhereby the range for Which the flashing means is sensitized may becontrolled by adjusting the angular position of the said second brush.

3. A manual range gate comprising a rotatable range scale, a fixed indexmounted independently of said range scale and adjacent thereto, flashingmeans to illuminate said range scale and index for stroboscopic readingof said scale in motion, a rotatable commutator having a short segmentand a long segment, means to rotate said range scale and said commutatorin synchronism and to maintain a constant angular relationshiptherebetween, a brush mounted independently of said commutator and inslidable electric contact therewith, means to adjust the angularrelationship between said brush and the said fixed index during rotationof said range scale and commutator, means electrically connecting saidbrush to said flashing means, means movably and electrically connectedto said short segment to sensitize said flashing means, and meansmovably and electrically connected to said long segment to disable saidashing means.

ALBERT M. SKELLETT.

